This invention relates to techniques for testing electronic systems. More particularly, this invention relates to methods for testing the mechanical and electrical attachment reliability of devices mounted to printed circuit boards.
Semiconductor devices are usually mounted to printed circuit boards and operate at relatively high temperatures. However, these elevated temperatures can lead to premature aging and failure of the devices, the printed circuit boards, and any other devices mounted to those circuit boards, especially with the continuing trend toward higher power devices. In order to avoid such failures in the field, extensive environmental testing in the laboratory has become an integral part of the design cycle.
A variety of techniques have been used to test the attachment reliability of devices mounted to circuit boards. For example, data analyzers, which have been used to monitor board interconnects subject to cyclic environmental loading, are available from Analysis Tech, a company located in Wakefield, Mass. In particular, these data analyzers can measure certain parameters essential for the design and implementation of reliable electronics. Such parameters include junction temperature and thermal resistance, as well as transient thermal response and die attachment quality. Normally, these parameters are measured during or after thermal cycling of the board to simulate thermal wear and tear. One disadvantage of these analyzers, however, is that they do not measure the mechanical parameters that are also critical for the design of reliable electronics.
A primitive method of simulating accelerated mechanical wear and tear in order to measure these mechanical parameters involves gripping the corners of the circuit hoard and twisting, or flexing, the board. This method does not accurately simulate device wear and tear, though, because a device is not being pushed or pulled, such as when a cable hangs from a connector. Moreover, this method cannot apply a controlled force to a single device without disturbing other devices on the board. Furthermore, the twisting method requires bulky mechanical apparatus to twist the board. This bulk may prevent a large number of boards from being placed in an environmental chamber simultaneously.
It is therefore an object of the present invention to provide an apparatus capable of accurately simulating one or more devices being pushed or pulled.
It is another object of the present invention to provide an apparatus capable of applying a controlled force to a single device mounted on the board without physically disturbing any other devices.
It is yet another object of the present invention to provide an apparatus that is relatively compact so that numerous circuit boards can be tested at once in a single environmental chamber.